application of laser-plasma accelerators

[email protected] Varenna Enrico Fermi Summer School 2011 [email protected] Varenna Enrico Fermi Summer School 2011

Application of Laser-Plasma Accelerators

Professor Dino JaroszynskiProfessor Dino JaroszynskiUniversity of StrathclydeUniversity of Strathclyde

Varenna LECTURES

[email protected] Varenna Enrico Fermi Summer School 2011

Outline of lectures• Lasers

• High Power Lasers

• Plasma

• Accelerators

• Applications

• Large and small accelerators

• How can we use a laser-driven plasma wave to produce coherent electromagnetic radiation?

• Laser driven wakes

• Ultra-short bunch electron production using wakefield accelerators

• Synchrotron, free-electron laser and betatron sources

• Conclusion and outlook


Selected review articles• S. Backus, C. G. Durfee III, M. M. Murnane, and H. C.

Kapteyn, “High power ultrafast lasers”, REV. OF SCIENT. INSTR. , 69, 1207 (1998)

• T. Katsouleas, “Electrons hang ten on laser wake”, Nature, 431, 515 (2004)

• V. Malka et al., “Principals and Applications of Laser-Plasma Accelerators”, Nature Physics, 4, 447 (2008)

• R. Bingham, “Basic Concepts in Plasma Accelerators”, Phil. Trans. of the Royal Society A 364, 559 (2006)

• Book: “Laser Plasma Interactions”, ed. D.A. Jaroszynski, R. Bingham and R.A. Cairns, CRC Press Taylor and Francis, ISBN 13:978-1-58488-778-2 (2009)


Basic Reference Material• Stanley Humphries, Jr., “Principles of Charged Particle

Acceleration”, John Wiley & Sons , New York, 1986, also available on-line.

• A. Chao and M. Tigner “Handbook of Accelerator Physics and Engineering”

• D.A. Edwards and M.J. Syphers, “An Introduction to the Physics of High Energy Accelerators”, John Wiley & Sons , New York, 1993.

• Helmut Wiedemann, “Particle Accelerator Physics”, Springer-Verlag, Berlin, 1993.

• Philip J. Bryant and Kjell Johnsen, “The Principles of Circular Accelerators and Storage Rings”, Cambridge University Press, Cambridge, 1993.

• Martin Reiser, “Theory and Design of Charged Particle Beams”, John Wiley & Sons , New York, 1994.


Lasers: High power, short pulse and high intensity

SUN

SHIN

E: 174 PW

Intensity:

I = 1018 Wcm-2Power:

P = 16 TW – world usage of power (≈100 km x 100 km sunshine)

Power

TW = 1012 W

GW = 109 W

MW = 106 W

KW = 103 W

Focus to a spot less than thickness of a human hair:Spot diameter 30 μm

Average Sunshine 120 Wm-2

Peak: 1.3 kWm-2

98 PW reaches the earth


Chirped Pulse Amplification

See Wiggins lectures


High Power Lasers: TW to PW

VULCAN Laser at Rutherford Appleton Laboratory

Power amplifiers Diffraction grating compressor


Lots of applications of lasers• material processing

• welding, cutting, drilling

• soldering,

• marking,

• surface modification

• laser displays (→ RGB sources)

• remote sensing (e.g. LIDAR)

• medical (e.g. Surgery)

• military (e.g. anti-missile weapons)

• fundamental science (e.g. particle acceleration)

• laser-induced nuclear fusion (e.g. in the NIF project)


Accelerators in use

• High energy accelerators (> 1GeV) >112

• Biomedical accelerators– Radiotherapy >4000

– Research including biomedical >800

– Medical radioisotope >200

• Accelerators in industry >1500

• Ion implanters >2000

• Surface processing >1000

• Synchrotron sources >50

• FELs >10

• Laser and beam driven plasma accelerators >5

• TOTAL >10,000


Lots of uses of accelerators• Study the structure of matter: colliders in the search for elementary particles

• Electromagnetic sources:

– X-rays for oncology (most widespread),

– synchrotron light sources and

– free-electron lasers

• Medical uses:

– Radiation therapy

– Radio-isotope production (for PET)

– Biological research

• Industrial uses:

– Ion implantation

– Photo-lithography

– Materials processing


Accelerators come in many guises

• Low energy – used to drive x-ray sources etc.

• Intermediate energy – Light sources: Synchrotrons and free-electron lasers– Energy amplifiers: accelerator driven sub-critical reactors: ADSR

– Material analysis – Rutherford backscattering, particle induced X-ray emission, nuclear reactions, elastic recoil, charged particle activation, accelerated mass spectroscopy

• High energy – Nuclear physics – probing nuclear structure

• Very high energy – energy frontier and astrophysics –Tevatron, LHC, muons as a source of neutrinos

• Secondary sources: gamma rays, neutrons, muons etc


A Brief History of Accelerators• Rolf Widerøe born in Oslo (1902 -1996)

– betatron and resonance accelerator

– betatron – based on magnetic induction

– resonance – based on resonant electric fields in cavities• John Cockcroft born in England (1897-1967)

• Ernest Walton born in Ireland (1903-1995)

– Linear accelerator – split atom• Robert J. van de Graaff (1901-1967)

– Static field accelerator• Ernest Lawrence US (1901-1958)

– Cyclotron


Particle and nuclear physics

• Energy creation

• Astrophysics

• Elementary composition of matter

• Origins of the universe

• Hadron colliders – to find new particles

• Lepton colliders – precise measurement of particles after their discovery


Medical application

• Treatment of cancer– X-rays, electrons, protons and ions

• Isotope generation – for PET

• Biological research – crystallography of large molecules: proteins, viruses etc.

• X-ray imaging: macroscopic and microscopic

Spectroscopy and imaging in Alzheimer research


Atomic physics, condensed matter, material science and chemistry

• Atomic collisions• Ionisation• X-ray production• Scattering• Neutron and ion beams• Elemental mapping• Charged particle activation• Radiation chemistry and radiolysis


Industrial applications• Studies of the structure of matter: chemistry and

biology• Trace element analysis• Ion implantation• Radiation processing (e.g. hardening)• Food preservation and sterilisation• Microlithography• Precision machining – ion beam milling• Cross-linking, polymerisation, depolymerisation,

grafting


Military applications

• Radar (microwaves from beams)

• Countermeasures (energy delivery, jamming)

• Beams (weapons)

• Remote sensing (surveillance and stewardship of nuclear material)


Power and energy

• Energy amplifiers (subcritical reactors)

• Nuclear fusion

• Power engineering

• Treatment of nuclear waste and control of nuclear proliferation (transmute dangerous and long-lived isotopes to short-lived isotopes)


Energy amplifier and waste transmutation

• Reactors produce poisonous by products: actinides –half-lives geological time scales

• Public worries about accidents, terrorist attack and proliferation

• Need high current proton accelerators• Energy amplifier – produces energy while transmuting

waste – possibility of using thorium to get around the proliferation problem

• Need about 1 GeV, 10 mA (10 MW beam)• Choice of accelerator crucial

– options: high current cyclotrons, synchrotrons, FFAG etc.


Fusion

• Options for fusion:– Magnetic confinement

– Laser inertial confinement• Fast ignition

• Indirect drive

– Ion fusion – indirect drive – 10 GeV heavy ion accelerators


Neutron sources

• Neutrons are complimentary to X-rays and electrons

• Condensed matter

• Molecular structure

• Penetrate deep into bulk (interact with nuclei)

• Less damage to biological material


Livingston plot

New ideas lead to new technologies

Acceleration gradient currently limits maximum energy

Laser wakefield accelerators?

(from tesla.desy.de)


Modern Livingston PlotFirst accelerator

Cyclotrons

Cockcroft-Walton electrostatic accelerators

Van de Graaff electrostatic accelerators

Betatrons

Synchrocyclotrons

Linear accelerators

Electron synchrotrons

Proton synchrotrons

Storage ring colliders

Linear colliders

Collider energy plotted as equivalent laboratory energy of particles colliding with a proton at rest to reach the same centre of mass energy

Snowmass report

Different technologies=New particles+Higher energies

A decade increase every 6 years


Limitations of present acceleratorsLimitations of present accelerators

GeV

TeV


Synchrotrons and free-electron laser light sources: tools for scientists & industrialists

Synchrotron – size and cost determined by accelerator technology

Diamond

undulatorsynchrotron & FEL

DESY undulator

Free-electron laser – coherent radiation: XFEL


CERN CERN –– LHCLHC27 km circumference27 km circumference

•

SLACSLAC

50 GeV in 3.3 km

20 MV/m

7 TeV in 27 km

7 MV/m

Large accelerators depend on superconducting Radio Frequency cavities and magnets


Conventional accelerators are based on RF cavities

• Conventional accelerator

SLAC

RF Cavities

Laser-plasma wakefieldAccelerator isx1000 smallerx1000 more accelerationx1000 less expensive

Plasma waves


Small accelerator based on plasma

Centimetre long plasma based accelerator

200 GeV/m


Laser-plasma accelerator development and application lab at Strathclyde: ALPHA-X

Generate radiation pulses on the ALPHA-X Beam Line

210

BENDINGMAGNET

UNDULATOR

ELECTRON ENERGYSPECTROMETER

LASER IN

PLASMA ACCELERATOR

RADIATIONSPECTROMETER


-4 -2 0 2 4k

1

2

3

4

5w

Waves in plasma

( )0( , ) i kz tt E e ωω − −=E

2 2 2 23p p B THk vω ω′ = +

2 2 2 2p k cω ω= +

vkφω=

Dispersion relationship

ωpWarm plasma: Bohm-Gross dispersion

Phase velocity: Group velocity: gdvdkω=


Relativistic effectsRelativistic effects The threshold for relativistic regime is a =1 where the field intensities are greater than 1018 W/cm2 for 1 μm lasers. The momentum of the electron increases due to the relativistic mass increase: ep m c>

The ratio of these two values defines the normalised vector potential90.85 10

e

pa Im c

λ−= = ×

The force and energy equations are given by the Lorentz equation: ( )d e

dt= = − + ×pF E v B

and relativistic energy equation:2( )ed m cd e

dt dtγ= = − ⋅E vE

From the Lorentz force electron motion becomes relativistic the electron describes a figure of eight path.

This due to the fact that 2 z× ∝ × ∝v B E B E

where I is given in W/cm2 and the wavelength in μm.


Self-focussing due to relativistic and ponderomotive effects

Plasma behaves as a dielectric medium with a dispersion relation governed by the plasma frequency

1/22

0

ep

e

n em

ωε γ⎛ ⎞

= ⎜ ⎟⎝ ⎠

γ is the time averaged relativistic factor γ = (1+a2/2)1/2.The higher the laser power the lower the plasma frequency.

The phase velocity in the plasma gives the refractive index1/ 22

20

1 pωη

ω⎡ ⎤

= −⎢ ⎥⎢ ⎥⎣ ⎦

When the laser frequency ω0 is less than the plasma frequency the field is evanescent and does not propagate in the plasma, thus the plasma frequency defines a cut-off frequency below which no transmission occurs.

Higher intensities lead to lower plasma frequencies and therefore lower cut-off frequencies. This means that a laser will penetrate further into an expanding plasma plume. The effect is sometimes termed relativistically induced transparency.


Relativistically induced guiding

The increase of the refractive index due to the relativistic causes relativistic self-focusing. The radial profile of a laser beam has a maximum on axis and therefore the refractive index will vary radially and act as a waveguide for the laser beam. When the focussing exactly matches diffraction, the laser beam will be guided.

The initially planar wavefront deforms in the plasma because the phase velocity vph=c/η is smaller on axis, causing the plasma to act as a positive lens and focus the beam. Guiding occurs when self-focussing is matched by diffraction. This occurs when P > Pc.


Relativistically induced transparency

An intense laser pulse with a frequency ω propagates in plasma with a phase and group velocity that is determined by the dispersion relation ω2 = ωp

2 + k 2c2, which depends on γ through ωp.

In dense plasma, with ω < ω p, light cannot propagate and is reflected from the surface.

However, at relativistic intensities with a large γ, the plasma can become transparent.

Dispersion relationship


Self-steepening

Because the group velocity, vgr=cη, increases where the intensity is highest the peak outruns the lower intensity parts of the laser pulse leading to self-steepening.

This leads to an optical shock, which is closely related to self-phase modulation of long laser pulses.

Because the front steepens, the ponderomotive force at the head of the pulse increases. This means that even though a laser may initially start with a low intensity, it can compress to become a very intense pulse, nearly an order of magnitude more intense.


Wakefield accelerator

Wake behind optical pulse travels and laser group velocity

2

20

1 pgv c

ωω

= −The ponderomotive force is given by the gradient of the light pressure

The electrons are pushed out of high intensity regions by the ponderomotive force

Group Lorentz factor

Critical density for 800 nm:

pondF P= −∇

( )2 2

2224pond

e dE dF mc am dz dzω

= − = −pλ

3-D plasma wave

UCLA: Tajima + Dawson 1979

2 2 01 / (1 / ) ωγω

= − =g gp

v c

21 31.75 10 cmcn −= ×

2ea eA m c=

20p p en e mω ε=


Particles accelerated by electrostatic fields of plasma waves

Accelerators:

Surf a 10’s cm long microwave –conventional technology

Surf a 10’s μm long plasma wave –laser-plasma technology 2

max

23

gaγγ ≈

[V/cm]E e n≈


Nonlinear wakes are similar with laser or particle beam drivers:3-D PIC OSIRIS Simulation

(self-ionized gas)

Laser Wake Electron beam Wake

Laser & Electron WakesLaser & Electron Wakes

[Simulations courtesy of Silva & Mori – Lisbon/IST & UCLA]


Wakefield acceleration: accelerating and focussing fields

λp


Modelling of Laser Wakefield Acceleration

laser pulse envelopeelectrostatic wakefieldbunch densityenergy density of wakefield

laser pulse envelope dynamics: ponderomotive wakefield excitation -electron bunch acceleration - phase slippage - beam loading

z-vg t (units of λp)

Strathclyde


Fourier spectrumof laser pulseplasma density modulation

laser pulse envelope

Laser pulse envelope dynamics and energy conservation

laser pulse amplitude: a0laser pulse energy depletion rate: ωd ~ a0

2 ωs

Linear regime: a0² « 1, ωd « ωs: pulse energy loss through photon decelerationwithout envelope modulation, static wakefield, low energy efficiency

Nonlinear regime: a0² ~ 1, ωd ~ ωs: pulse energy loss through photon decelerationand strong envelope modulation, dynamic wakefield, better energy efficiency

z-vgt (units of λp) k / k0


• Dephasing:

Limits to Energy gain: Limits to Energy gain: ΔΔW=W=eEeEzzLLaccacc

•• Diffraction:

20

20

max

23

pd g L

g

L a c

a

γ τ

γγ

≅

≅

0g L

p p

ω πγ τω ω

= ≈• Pump Depletion:

For small a0 Ldp >> LdphFor a0 ≥ 1 Ldp ~ Ldph

2 20 /Rz wπ λ=

~ millimeters!(but can be avoided using plasma channels or relativistic self-focusing)

cvg

20

21

43

pdph

gr

gdph

p

Lv c

c aL

λ

γω

=−

=

~ 10 cm x 1016/no

( ) 2/3 [GeV] ~ 0.038 [TW] crE P P −

2~ 17 [GW]cr gP γ


r 0 = 150 μm capillary

n (0) = 1018 cm-3

I > 1017 W/cm2

Plasma formed by electrical discharge between electrodes

Plasma capillary waveguide

2

0 20

12 4

0

( )

me

rn r n nr

rwr n

δ

π δ

= +

⎛ ⎞= ⎜ ⎟⎝ ⎠

phase-matching: tapered capillary

Capillary: preformed plasma waveguide

electrodes


Plasma waveguide formation

•After t ~ 80 ns plasma in quasi equilibrium. •Ohmic heating of plasma balanced by conduction of heat to wall

[ ] [ ]( )

51/43

1.5 10M

e

a mw m

n cm

μμ

−= ×

⎡ ⎤⎣ ⎦

21 0ed dTr E

r dr drκ σ⊥ ⊥

⎛ ⎞ + =⎜ ⎟⎝ ⎠

Solution of the heat flow equation yields scaling relation for matched spot size:

See D. J. Spence & S. M. Hooker Phys. Rev. E 63 015401 (2000)


– Electron density measured with Mach-Zender interferometer

– H2 pressure is 63 mbar.– Central section

parabolic electron density profile: matched spot size 37 mm.

– >90 % transmission over 4 cm channel

– > 105 shots

D. J. Spence & S. M. Hooker Phys. Rev. E 63 015401 (2000)

2

0 20

( ) rn r n nr

= + Δ

Plasma-filled capillary waveguide electron density profiles

t = 60 ns

Oxford


Manufacture of plasma capillaries for laser wakefield

accelerators300 μm

Developed at Strathclyde

After one year…..(Jaroszynski et al., Royal Society Transactions, 2006)

This method of manufacture is now used by all groups using plasma capillaries


Guiding in plasma capillaries

400 mm

~ 60 μm dia.~ 60 μm dia.

Strathclyde


Equations of motion in harmonic potential

For relativistic particles, the trajectory is governed by the equations

, , γ= = =d d mdt dtr Pv F P v where

V( )= −∇rF r

is the Lorentz factor.2 2

2 2

1 1 /( )1 /

P mcv c

γ = = +−

If force can be written as a gradient of a potential

then the equations are Hamiltonian H, H.= ∇ = −∇P rd ddt dtr P

with conserved energy 2H Vmcγ= + as Hamiltonian

(Theory lectures based Strathclyde undergraduate lectures)


Hamiltonian: pendulum equation

θ

mass m

2

2 sin 0d gdt l

θ θ+ =

length l

gravF mg=

strF

θ

dθ/d

t(g

/l=1)

21 cos2

d gHdt lθ θ⎛ ⎞⇒ = −⎜ ⎟

⎝ ⎠

phase space diagram


Examples of 1-D wakefields:Linear and non-linear

wakefield profiles in the frame moving with the laser pulse:linear andnonlinear regimes

red: intensity Igreen: electric field Ezblue: density perturbation δn

t-z/vg (fs)

t-z/vg (fs)


EfficiencyEfficiency

−500 −400 −300 −200 −100 0

−0.5

0

0.5

1

−500 −400 −300 −200 −100 0

−0.5

0

0.5

1pulse

intensity

accelerating wakefield

wakeenergy density

bunch density

at injection just after dephasing

(fs) /cζ

• Effect of bunch wakefield = beam loading• Important for wake-to-bunch energy transfer• Finite charge required for energy absorption from the wakefield

• ideal (almost 100%) conversion of wake energy into bunch energy• all electrons accelerated• → bunch slips out of ideal position• → large spread of accelerating field induces large energy spread

• slight loss of energy from bunch to wake• most electrons decelerated• complicated structure of accelerating field along electron bunch


Wakefield efficiency

0 5 10 1540

60

80

100

0 5 10 150

0.25

0.5

0 5 10 150

2

4

6

ct (cm)

Pulse energy (%) Wake amplitude (norm.) Peak value of |a|2

a02=0.25

0.50.75

1

1 1

0.750.75

0.5 0.50.250.25

simulated with laser envelope / quasi-static plasma fluid modelct (cm)ct (cm)

• At low amplitude, the LWFA scheme suffers not only from a lower energy gain, but also from low efficiency.• Energy transfer from plasma wave to electron limited by dephasing –electron runs into decelerating region due to vg<c - this determines the acceleration length.• Energy transfer from laser pulse to plasma wave is governed by feedback (instability), which develops faster at high a0.

Example: 1-D simulation results for Gaussian laser pulse with resonant pulse length, plasma density 1018 cm-3, and 4 different pulse amplitudes.


Examples 2-D plasma wakefields

linear regime, uniform plasma

kpx

kp(z-vgt)nonlinear regime, uniform plasma

Ez δn

linear regime, plasma channel


0, 0 , 0 , 0∂ − ∇ × = ∇ ⋅ = ∂ + ∇ × = ∇ ⋅ =t tc cE B B B E E

Travelling electromagnetic waves

( ) ( )0 0cos , coszA A kz t kz tω ϕ ϕ ω= − = −

Maxwell’s equations reformulated with potentials (A,φ)

[ ] ( )2 2 2/ , , 0.ϕ ϕ⎡ ⎤= − ∂ + ∇ = ∇ × ⇒ ∂ − ∇ =⎣ ⎦t tc cE A B A A

in Lorentz gauge: 0ϕ∂ + ∇ ⋅ =t c A

Plane-wave solutions: transverse wave

( )0 0, / 0.z t z zck A E A cω ϕ ϕ= = ⇒ = − ∂ + ∂ =

No acceleration from transverse E-field• Need RF waveguide – TM modes have longitudinal E-field component• Need wave in a medium – e.g. structured solid (crystal) or plasma

Tesla superconducting cavities

RF fields


Acceleration in travelling wave

0 0sin( ) sin( [ ( ') ' ]) t

dP F kz t F k v t dt v tdt φω= − = −∫

Constant force - resonance condition: at all values of t, ( ') 't

v t dt v t Cφ= +∫only possible if vφ time-dependent, else dP/dt=0 (no acceleration).

vz ≈ c

vφ < c

t=0

t=t1

Motion of particles with speed close to c in a wave travelling at speed vφ < c.

Dephasing limits acceleration time to advance over ½ wavelength:

Acceleration: dP/dt>0Deceleration: dP/dt<0


Acceleration in travelling wave continued…

Calculation of maximum ΔP:

- position z = z1+ct - force at t = 0 is F0sin(kz1) = 0 if sin(kz1) = 0- advance ½ wavelength - force returns to 0 at t = t1 = π/(kc-kvφ) - equal to 2π γφ

2/kc if vφ ≈ c

2 20 0 0 00

( / ) sin( ) 2 /P P F c d P F cπ

φ φλγ α α λγ⇒ = + = +∫

phase space diagram illustrates motion of particles with vz ≈ c

/ gγ γ

( ) /z v tφ λ−


Electrons in harmonic potential: ponderomotive or Coulomb potential

00 0

penen zEλδ

ε ε= =

Assume that the electrons are travelling very close to the phase velocity of the field, ω/v k and that electrons are close to the trough of the potential then ζ ζ≅sink k

and ζ ζ= − eEk

mwhich describes simple harmonic motion with a bounce frequency

ω =B

eEkm

Wave-breaking occurs when the bounce frequency approaches the plasma frequency, i.e. when Gauss Law: ω ω≅

B p

i.e. when 0 2( 1)γ= −WB gE E where 1/2 30 ( / ) 0.96 [cm ]V/cme p eE m c e nω −= ≈

γg is the relativistic factor corresponding to the plasma phase velocity, vg.

EWB can be obtained from Gauss’s law, eE0 ~ mcωp . When the wave breaks electrons suddenly increase their energy spread and cause the electromagnetic wave to lose energy. Plasma wave grows and becomes non-sinusoidal and steepens resulting in a singularity in the electron density.


Electron acceleration: catching the wave

Electrons are accelerated in wakefield if their initial velocity is sufficiently close to the phase velocity of the wakefield for trapping occurs i.e.

The electron motion: velocity and acceleration:

2, zz g

ds dP dv v mcdt dt ds

ψ= − = −

vgvz


Electron motion

/ gγ γ

/ ps λγgmc2 corresponds to an electron moving at the phase velocity of the wakefield, given by

( )s t ( )tγ

/ dt t / dt t

0pik se eψ −=


Acceleration in potential: Acceleration in potential: dephasingdephasing for for weakly nonlinear caseweakly nonlinear case

Energy gain limited by dephasing, caused by difference between velocities of electron and wakefield

Scaling favours low plasma density

gwfel vvcv ≈>≈12/32/1 −− ∝∝×∝Δ pppdeph nnnLEγ

−500 −400 −300 −200 −100 00

3

6

9

log(γ)

(fs) /cζ

electron orbit

laser pulse intensity

separatrix

Note: logarithmicenergy scale


EfficiencyEfficiency

• ideal (almost 100%) conversionof wake energy into bunch energy

• all electrons accelerated• wakefield to zero at rear part of bunch

- bunch slips out of ideal position- large spread of accelerating field

induces large energy spread

• slight loss of energy from bunch to wake

• most electrons decelerated• complicated structure of

accelerating field along electron bunch

effect of bunch wakefield = beam loading• central to wake-to-bunch energy transfer, • finite charge required for energy absorption from the wakefield

−500 −400 −300 −200 −100 0

−0.5

0

0.5

1

−500 −400 −300 −200 −100 0

−0.5

0

0.5

1pulse

intensity

accelerating wakefield

wakeenergy density

bunch density

at injection just after dephasing

(fs) /cζ


Beam loading & energy spreadElectron bunch induces wakefield.

Total wakefield is sum of laser wakefield and bunch wakefield.

Amplitude difference is a measure of energy transfer.

Beam loading sets charge limit. For acceleration, amplitude of bunch wakefield must remain smaller than amplitude of wakefield.

Fully compressed bunch with finite charge induces jump in accelerating gradient.

s

s

F

F


Energy spread and stability: measurements at Strathclyde

Mean energy drops with increase in charge:Beam loading

Energy spread increases with charge

Stability:

130 135 140 145 1500

5

10

15

20

25

30C

ount

s

Energy [MeV]

r.m.s. spread of mean energy 2.8%


Bubble scaling: highly relativistic case• Bubble radius is approximately equal to the

• relativistic plasma wavelength:

• λp becomes giving• The dephasing length is determined by the bubble radius: electrons catch up with the bubble centre.

• The laser propagates at the group velocity but plasma piles up in front of it causing a barrier and an increase in plasma density.

• This causes the laser to etch back at a velocity:

• So the laser group velocity becomes

pRλπ

=

0 pa λ 0 paR

λπ

=

2etchg

cvγ

=

2 2 2

1 1 31 12g g etch

g g g

v v v c cγ γ γ

⎛ ⎞ ⎛ ⎞′= − = − − ≈ −⎜ ⎟ ⎜ ⎟⎜ ⎟⎜ ⎟ ⎝ ⎠⎝ ⎠

Use expansion (1-x)1/2 ≈ 1-x/2


Dephasing and depletion lengths: highly relativistic case (Bubble regime)

Dephasing length can be calculated from

Therefore

We can also estimate the pump depletion length: i.e. over which the laser pulse is etched away. This is given by

The laser spot size should be matched to the bubble diameteri.e.

Relativistic self-guiding occurs if

or for a matched beam.

Energy gain can be easily calculated:

≈−d

g

cL Rc v

223

gdL R

γ≈

2FWHM

etch FWHMetch g

c cL cv

ττγ

≈ ≈

0w R≈

( )20

2

0

4or8c

p

aP Pk w

≥ ≥

00

paλλ

≥2

0max 0

23 p

aωγω⎛ ⎞

≈ ⎜ ⎟⎜ ⎟⎝ ⎠


ALPHA-X all-optical injection experiments on ASTRA

3%δγγ

≈800 nm

350 – 540 mJ

40 fs

F/16 mirror

1018 Wcm-2 in 25 μm spot

a0 ~ 0.7 – 1

ne~ 2 x 1019 cm-3

S. Mangles et al. Nature 2004

Imperial/RAL/Strathclyde

τ~ 5 – 10 fsI ~ 5 kA


Jena measurements

Thomson scattering of the channel above the gas nozzle

Channel location in the plasma profile

spectrum on x-ray film

MPQ

274 μm

E: 0.75 – 1 J, I ~ 1020 W/cm2.Parabolic mirror: f/2.5, Spot size ~ 5 μm2

Pulse duration: ~ 75 – 80 fs, λ = 800 nm n ~1019-1020 cm-3 (Helium).

Δγ/γ∼3%

Sauerbrey, Schwoerer, MPQ and ALPHA-X team


LBNL - Oxford campaign(ALPHA-X) team: GeV beams from capillary

Robust capillary channels manufactured using methods developed at Strathclyde (Jaroszynski et al., Royal Society Transactions, 2006)

Pre-formed plasma channels –Spence & Hooker (PRE 2001)

W. Leemans, et al., (Nature Physics 2006)


1 GeV beams

W. Leemans, et al., (Nature Physics 2006)


Energy spread and emittance

• Non-ideal electron beams degrade radiation properties: reduces brilliance and lowers FEL gain

• Emittance: area in transverse phase space

• Approx. beam size times RMS beam divergence

• Normalised emittance: needs to be 1 π mm mrad

• Energy spread: needs to be 0.1% for a free-electron laser

• The rms emittance gives the minimum beam size that can be achieved

, , ,x y x y x yε σ σ ′≈

nε γβε=

γσγ


RMS emittance

The rms emittance gives the minimum beam size that can be achieved

( )222, rmsrmsrmsrmsu uuuu ′−′⋅=ε

The normalised emittance is defined as :

which is conserved for accelerating beams

uunuu ′′ ⋅= εβγε ,


Transverse Brightness

• Quality of electron beam given by normalised brightness

• I = peak current, εnx,y = normalised emittance

• Pencil shaped beam εnx= εny , J=I/σr2

• Beam waist

• Beta function β (analogue of Rayleigh range)

• Brightness

2n

nx ny

IBε ε

=

nr

ε βσγ

=

2

2 22 2

( )r

nn

J JB σσ γ ε

= =′

β

σrσ'=σr/β


• 500 consecutive shots• narrow divergence (~2 mrad) beam• wide divergence halo• θX = (7 ± 3) mrad, θY = (3 ± 2) mrad

• 8 mrad acceptance angle for EMQs• 25% pointing reduction with

PMQs installed

-10

0

10

20

-10 0 10 20

θ Y[m

rad]

θX [mrad]

no PMQs PMQs in

5 mrad

Experimental Results – beam pointing


Emittance of Strathclyde beam

0 50000 100000

-1.0 -0.5 0.0 0.5 1.0

-3

-2

-1

0

1

2

3

counts

(b)

x' [

mra

d]

x [mm]

θxσx

xσx

x

x′

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5

-6

-4

-2

0

2

4

6

0 5000 10000

x' [m

rad]

x [mm]

counts

• divergence 4 mrad• εN,x < (5.5±1) π mm mrad

• divergence 6 mrad• hole size correction• limited by detection system• εN,x < (7.8±1) π mm mrad

A measure of the upper limit of emittance

Shanks et al.,Proc. SPIE 735907 (2009).


-0.75 -0.50 -0.25 0.00 0.25 0.50 0.75

-3

-2

-1

0

1

2

3

4

x' [m

rad]

x[mm]

Experimental Results – emittance

• divergence 1 – 2 mrad for this runwith 125 MeV electrons

• average εN = (2.2 ± 0.7)π mm mrad• best εN = (1.0 ± 0.1)π mm mrad• Elliptical beam: εN, X > εN, Y

•E. Brunetti, et al., PRL 2010

• Second generation mask with hole φ ~ 25 μm and improved detection system

0 1 2 30

5

10

Cou

nt

εnx [π mm mrad]

(a)

0 1 2 30

5

10

Cou

nt

εny [π mm mrad]

(b)


Strathclyde: Measured energy spread

0.7%γσγ

=

Further accelerate to 1 GeV would give

beam loading simulations →

Shot to shot variation in mean energy: . . . 6%r m sγγ

Δ ≈

60 MeV 100 MeV

Wiggins et al., SPIE Proc. SPIE 735914 (2009)

0.05%γγ

Δ <

70 75 80 85 90 95 1000

250

500

750

1000

No.

ele

ctro

ns/ M

eV [a

.u.]

Electron energy [MeV]

(b)


Experimental Results – energy spectra III

65 70 75 80 85 90 95 1000

1000

2000

3000

4000

5000

Cha

rge

(a.u

.)

Energy (MeV)

σγ/γ MEAS= 0.7%

0

0.1

0.2

0.3

0 1 2 3

Res

olut

ion

[%]

Initial Emittance [π mm mrad]

No PMQs

With PMQs

60 80 100 120 140 160 1800

102030405060

Cha

rge

(a. u

.)

Energy (MeV)

0123456

0 0.5 1 1.5 2 2.5 3R

esol

utio

n [%

]Initial emittance [π mm mrad]

simulationat 146 MeV

σγ/γ MEAS= 0.4%

• Indicates fixed absolute energy spread ~ 600 KeV

simulationat 85 MeV


Experimental Results – charge

LANEX 2Imaging Plate

y = 2.488xR² = 0.953

0

2

4

6

8

0 1 2 3

Imag

ing

Plat

e Ch

arge

(pC)

Lanex 2 counts (x 108)

Cross-calibration in progress


Extending to higher energy:Strathclyde plasma media

• Extend energy range to multi GeV• Study plasma media – extend length relativistic self focussing, gas cells and channels• Stable electron beam generation

4 cm


Typical high energy spectra: RAL-Gemini experiment using plasma channel 85% of shots


Radiation sources: Synchrotron and Free-electron laser (FEL):

a potential compact light source

• Use output of wakefield accelerator to drive compact synchrotron light source or FEL

• Take advantage of electron beam properties

• Coherent spontaneous emission: prebunched FEL I~I0(N+N(N-1)f(k))

• Ultra-short duration electron bunches: I >10 kA

• Operate in superradiant regime: FEL X-ray amplifier (self-similar evolution)

Potential compact future synchrotron source and x-ray FEL

• Need a low emittance GeV beam with < 10 fs electron beam with I > 10 kA

• Operate in superradiant regime: SASE alone is not adequate: noise amplifier

• Need to consider injection (from HHG source) or pre-bunching


Synchrotrons

• 1-8 GeV – X-rays to THz interact with electronic structure– THz – low frequency modes

– VUV – molecular structure– X-ray spectroscopy

– Extended X-ray Absorption Fine Structure – EXAFS– X-ray diffraction

– Imaging and microscopy

• Bending magnets, undulators and wigglers

DIAMOND

Diamond Cryogenic undulator


Undulator


Synchrotron Radiation Properties I

• Bending magnet:

232c

e Bm

γω =


Synchrotron Properties II

Wiggler and undulator

10-9 10-8

0

1

2

Wavelength [m]

au = 0.6Po

wer

[x10

-6 p

er u

nit f

requ

ency

and

sol

id a

ngle

]

10-9 10-8

0

1

2

au = 1

10-9 10-8

0

1

2

au = 2

10-9 10-8

0

1

2au = 3

2

02

2 20

22 where

where 1

2and is observation angle or beam angle

u z uu

z uu u e

k c k

eBaa k m c

πω γλ

γγγ θ

θ

= =

= =+ +

2

2 2

0

3 1 critical harmonic4 2

6where is the currentand is the number of periods

u uc

u u uT

u

a an

ea IN kP

IN

γε

⎛ ⎞= +⎜ ⎟

⎝ ⎠

= total angle

1 1 where

u

cuu

a

NN

θγ

ωθωγ

=

Δ= ≈

4

0.5%

10 rad

γσγ

θ −

=

=


Compact synchrotron source

• Undulator radiation emitted into cone

• Wavelength: and

• Normalised undulator potential

22 2

21(1 );

2 2 2u u

u

aN

λ λλ γ θγ λ

Δ= + + ≈

1θγ

≈

ˆ

2u

ueBa

mcλ

π=

1

uN γ

Strathclyde

λu – undulator wavelength


First compact wakefield driven synchrotron source

wakefield accelerator undulator

spectrometers

Strathclyde & Jena

Strathclyde collaboration with IOQ Jena

Supported by EPSRC, E.U. Laserlab and EuroLEAP

H-P Schlenvoigt, .. D.A. Jaroszynski: Nature Physics 2007/2008


Electron and radiation spectra

Nph~300,000 photons

Q = 28 pC @ 65 MeV

ϕ = 2 mrad

δλ/λ = 55 nm (FWHM)

B = 6.5x1016

ph/sec/mrad²/mm²/0.1%BW

σγ/γ=2%

( )1/ 22 2 2 2 2/ 0.5 / ( ) 1/ umeasured

Nδγ γ δλ λ ϑ γ⎡ ⎤< − −⎣ ⎦

Sets an upper limit to total energy spread (≈1%) and emittance (1 π mm mrad)H-P Schlenvoigt, .. D.A. Jaroszynski: Nature Physics

2007/2008

Strathclyde, Jena & Stellenbosch


Scaling with energy

22 2

2 12 2

u uahλλ γ ϑγ

⎛ ⎞= + +⎜ ⎟

⎝ ⎠

Extrapolate to 1 GeV:

400 eV photons

B = 2 x1023




World first undulator radiation from LWFA demonstration

• Strathclyde, Jena, Stellenbosch collaboration• 55 – 70 MeV electrons• VIS/IR synchrotron radiation

• Measured σγ /γ ~ 2.2 – 6.2%• Analysis of undulator spectrum andmodelling of spectrometer

σγ /γ closer to 1%

Schlenvoigt .., Jaroszynski et al., Nature Phys. 4, 130 (2008)Gallacher, ….Jaroszynski et al. Physics of Plasmas, Sept. (2009)


Electron and optical spectra:undulator as an electron

spectrometerStrathclyde, Jena & Stellenbosch

H-P Schlenvoigt, .. D.A. Jaroszynski: Nature Physics, 2008


Scaling with energy

22 2

2 12 2

u uahλλ γ ϑγ

⎛ ⎞= + +⎜ ⎟

⎝ ⎠

h – harmonic number

Extrapolate to 1 GeV:

400 eV photons

B = 2 x1023




Free-electron laser driven by wakefield accelerator

• Combination of undulator and radiation fields produces ponderomotive force which bunches electron on a wavelength scale

• Laser field grows exponentially at a rate governed bythe electron beam gain coefficient: ρ = 1.1 γ -1Bu λu

4/3Ipk1/3 εn

-1/3

• Gain length

• Need slice energy spread δγ/γ<ρ and slice emittance εn<4λβγρ/λu or εn<γλ(matched)

• Slice length: cooperation length: 30 – 100 periods i.e. <1 fs for x-rays – several pC

2 3u

gL λπ ρ

=

2

2 12 2

u uaλλγ

⎛ ⎞= +⎜ ⎟

⎝ ⎠

See Bonifacio et al. (Nuova Cimento 1990, 1992)


Synchrotron and FEL radiation peak

brilliance

ALPHA-X ideal 1GeV bunch

FEL: Brilliance 5 – 7 orders of magnitude larger

λu = 1.5 cm

εn = 1 π mm mrad

τe = 10 fs

Q = 100 – 200 pC

I = 25 kA

δγ/γ < 1%

I(k) ~ I0(k)(N+N(N-1)f(k)) FEL = spontaneous emission x 107


Probes of matter


Synchrotron application of X-rays

• X-ray diffraction: surface, bulk, large molecule, and interface– Structure of macromolecules: enzymes, proteins etc.– Solid state: Crystal, semiconductor and non-crystalline

structure – new materials, superconductors etc• X-ray spectroscopy

– Fluorescence, dichroism– photo-emission

• X-ray microscopy– Microfocus, spectromicroscopy

• X-ray tomography


Biology

• Protein and enzyme structure

• Basic biological structure

• Drug development

• Physiology


Betatron motion Periodic transverse

forces of wakeλp

LASER

• Transverse oscillations in focusing regions are called betatron oscillations

• Betatron frequency and amplitude depends on longitudinal phase and energy

ωβ

x


Betatron radiation


Increase in wiggler parameter

10-9 10-8

0

1

2

Wavelength [m]

au = 0.6

Pow

er [x

10-6 p

er u

nit f

requ

ency

and

sol

id a

ngle

]

10-9 10-8

0

1

2

au = 1

10-9 10-8

0

1

2

au = 2

10-9 10-8

0

1

2au = 3

338

β≈crit

an


Betatron radiation as a gamma ray source

• Transverse oscillation in ion channel: • wiggler-like emission

• Ion channel radiation: Whittum et al., PRL 1990

X-ray beamGas jet

20 mrad

Ephoton>3 keV

106 ph/shot/0.1% BW

(30 fs, 20 mrad, > 3keV)

Rousse et al., Phys. Rev. Lett. (2004)Puhkov et al., Phys. Rev. Lett. (2004)Esarey et al., PRE (2002)


Plasma wiggler

• Wiggler motion – electron deflection angle θ ~ (px/pz) is much larger than the angular spread of the radiation (1/γ)

• Only when k & p point in the same direction do we get a radiation contribution.

• Spectrum very rich in harmonics – peaking at

1βγ >> >>a

Deflection angle – au/γ

Ω = 1/γ

338

β≈crit

an


X-ray generation in a plasma wake• Strong radial forces cause synchrotron or betatron oscillations of electron beam

• Ion channel radius: electrostatic field

• Dense pencil electron beam – radius re<<ri and re<<1/kp

• Restoring force given by Gauss law: •• Oscillation at the betatron frequency (in bubble):

• Emitted synchrotron radiation viewed in the lab frame

h – harmonic number

• hcrit - maximum intensity at harmonic

• Undulator/wiggler deflection parameter

ei e

p

nr rn

≈

212 pF m rω ⊥= −

02p

r

n erE

ε=

2 22 2

2 3/231 ( ) 1 ( )

2 2 2h e ee p e

a ach h

β β βλ πλ γ ϕ γ ϕγ ω γ

⎛ ⎞ ⎛ ⎞= + + = + +⎜ ⎟ ⎜ ⎟

⎝ ⎠ ⎝ ⎠

338crit

ah β≈

29phot fN aβπ α=

2 / 3 pa rβ βγβ π γ λ⊥= =

γω

ωβ 2p=


Direct laser acceleration

• Transverse oscillations in the ponderomotive

potential occurs at the betatron frequency

• When the laser field observed in the moving frame of reference is resonant

with the betatron frequency where

• Then the electron can experience a constant force and gain a huge amount of transverse momentum.

• The Lorentz force with the laser magnetic field can lead to a transfer of transverse to longitudinal momentum without adding further energy

2p

β

ωω

γ=

022 z

βωωγ

=

×v B

From Pukhov et al. Phys. Plasma 6, 2847 (1999)

02

12β

γγ =

+z

a


Extending to higher energies:

10 100 1000X-ray energy [KeV]

02×

10-6

4×10

-66×

10-6

X-r

ay e

mis

sion

[ar

b. u

nit]

rβ~ 3 μm

rβ~ 8 μm

rβ~ 14 μmcalculation

338

β≈crit

an

2β β

γ πγ

λ= = e e

e ep

ra k r


Dependence on initial electron distribution


Positron source (UCLA –SLAC) using betatronradiation

Johnson, Clayton et al. 2005


pλγλβ2/1)2(=

Betatron period Number of photons

Strength parameter K = au

X-ray beam

20 mrad

EX>3 keVPhys. Rev. Lett. 93,

135005 (2004)

X-ray sources Synchrotron radiation in a mm-scale plasma

106 ph/shot/0.1% BW

New pioneering tool for ultrafast x-ray science

Broad spectrum: x-ray absorptionCollimation: improved focusing

efficiency on sampleTunable: x-ray diffraction

PXF group, A. Rousse, http://loa.ensta.fr/pxf

(30 fs, 20 mrad, > 3keV)

First beam of x-rays using lasers


ExperimentPIC

No electrons - Plasma wave weak

Electron spectrum

Signal on X-ray CCD

Less electronsLess energetic

150 MeV

Broken wave regimeEnergetic electrons

150 MeV

Betatron X-rays

Phys. Rev. Lett. 93, 135005 (2004)

Kim TA PHUOC & Antoine ROUSSE


Betatron Radiation Properties

F. Albert. T. Phoucet al. Plasma Phys. Control. Fusion 50 (2008) 124008 (9pp)

S. Kneip et al, Nature Physics,6 (2010)


How to produce coherent radiation? the free-electron laser

• Coherent, very high brightness beam

• Tuneable: THz-IR-UV-X-rays

• Short pulse

• Synchronised with other sources (lasers, particle sources) – can be aggregated to create toolbox

• LCLS, XFEL, SCSS, PSI-XFEL etc.X-ray holography at LCLSEuropean X-FEL

Undulator for SCSS: Spring-8 Compact SASE Source

JLA

Energy recover linac FEL


Undulator


FEL

• Tuning range the same as undulator or wiggler radiation

Coherence due to bunching enhances brilliance by many orders of magnitude


Free-electron laser• Combination of undulator and radiation fields produces ponderomotive force

which bunches electron on a wavelength scale

• Laser field grows exponentially at a rate governed by• Matched electron beam gain coefficient: ρ = 1.1 γ -1Bu λu

4/3Ipk1/3 εn

-1/3

• Gain length

• Need slice energy spread δγ/γ<ρ and slice emittance εn<4λβγρ/λu or εn<γλ(matched)

• Slice length: cooperation length: 30 – 100 periods i.e. <<1 fs for x-rays – several pC

2 3u

gL λπ ρ

=

2

2 12 2

u uaλλγ

⎛ ⎞= +⎜ ⎟

⎝ ⎠

See Bonifacio et al. (Nuova Cimento 1990, 1992)


Free-electron laser

•λ ~ 1.5 nm x-ray FEL requires ∼1 GeV

•Growth of an injected or spontaneous field in a FEL amplifier is given by I = I0 exp(gz),

•g = 4πρ31/2/λu – small signal gain,

•ρ - FEL gain parameter - a function of the beam energy, current and emittance.

•εn = γ σ′σ is the normalised slice emittance of the beam.

•ρ ~ 0.001 for electron beam parameter but need slice energy spread δγ / γ < ρ i.e. <0.1 %


Electron energy (MeV)

Radiationλ

(nm)

Emittance criterion

(π mm mrad)

Gain parameter

ρ

Relative energy spread

90 261 3 0.011 0.007

150 94 2 0.006 0.004

500 8 0.6 0.002 0.001(?)

LWFA-driven FEL

• High FEL gain criteria: εn < λγ/4π & σγ/γ < ρ• Experimental εn ≤ 0.8π mm mrad & σγ/γ ≤ 0.007• For fixed σγ = 0.6 MeV, σγ/γ reduces at short λ

3/12

221

⎥⎥⎦

⎤

⎢⎢⎣

⎡⎟⎟⎠

⎞⎜⎜⎝

⎛=

x

uu

A

p aII

πσλ

γρ

λu = 15 mm, N = 200, au = 0.38

ALPHA-X Undulator

STEADY STATE SIMULATION RESULTS (100 MeVelectrons)Saturation power(1st harmonic): 20 GW@ saturation distance: 1.8 m

UNDULATOR RADIATION EXPERIMENTSIn progress for improving beam transport and observing gain

R. Bonifacio et al., 1984


Synchrotron radiation and SASE FEL for same parameters

350 400 450

0

1x1012

2x1012

3x1012

Phot

on F

lux

[Pho

tons

/0.1

% B

W]

Photon energy [eV]

SASE FEL

350 400 450

0.0

5.0x105

1.0x106

1.5x106

Phot

on F

lux

[Pho

tons

/0.1

% B

W]

Photon energy [eV]

Peak Brilliance: 2.97 x 1025 photons/sec/mrad²/mm²/0.1%b.w.

Photon flux into 200 μrad

matched beam SASE FEL

synchrotron radiation

Synchrotron:

Peak Brilliance B = 3 x 1025

ph./sec/mrad2/mm2/0.1% b.w. for 10 Hz

Average brilliance B = 2.5 x 1011

With laser improvements: 1 kHz: rep rate: average brilliance B >1013

FEL: B >106 times higher

σγ /γ = 0.1%

Ipk = 12 kA

εn = 1 πmm mrad

Nu = 200

τe < 10 fs


Predicted SASE FEL Power growth

E = 1 GeV

Q = 100 pC

Ipk = 30 kA

εn = 1 π mm mrad

δγ/γ = 0.1%

β = 0.5 m

ρ = 0.0065

Eph = 422 eV

Bpk = 6 x 1031

phot/sec/mm2/mrad2

/0.1% BW

6.3 x 1012

coherent photons per pulse


Tuning range

FELs give huge increase in brilliance


More applications


Fourier transform holography

• X-ray pinhole camera with a shutter speed of a few femtoseconds

• Holograms of nanoscale objects• “Coded apertures” can image

without focussing optics• X-rays transmitted through array of

holes interferes with radiation through (micron sized) sample

• Hadamard transform to deconvolveimage

• Resolution determined by photon energy and scale of array - very high resolution possible

• See S. Marchesini et al., Nature Photonics, doi: 10.1038/nphoton.2008.154 (2008).


X-ray diffraction

• FLASH – DESY experiments

• Chapman et al. Nature Physics 2 839 (2006)

• Need Ångströmwavelength X-rays X-ray Diffraction pattern at

FLASH DESY


Medical applications

• Treatment of cancer– X-rays, electrons, protons, neutrons and ions

• Isotope generation for PET (Positron Emission Tomography) and SPECT (Single Photon Emission Computed Tomography)

• Biological research – crystallography of large molecules: proteins, viruses etc.

• X-ray imaging: macroscopic and microscopic

Spectroscopy and imaging in Alzheimer research


Radiotherapy I

• >1 m people develop cancer every year in Western Europe• Radiotherapy treatment goes back to 1890’s - Röntgen and Curie

– Effective and physically selective - geometry• 45% of cancers can be cured

– 50% of these by radiation therapy alone, or combined with chemotherapy and/or surgery.

• X-rays from 5-20 MeV linacs used in most cases– 3-D Conformation therapy – multiple beams improve treatment

• Electron beam therapy (used for 10-25% patients)– Superficial tumours– Intra-Operative-Radiation-Therapy (IORT) used in surgery

• Proton and ion therapy – in development


Radiotherapy II

• Radiotherapy damages DNA: Double-break DNA strands

• Directly – photon, electron, protons, neutron or ion beams

• Most common: Indirectly ionising DNA – by ionising water to form free radicals (hydroxyl radicals), which damages DNA.

• Cancer cells are undifferentiated (unspecialised) and stem-cell-like – reproduce rapidly but have diminished ability to repair sub-lethal damage compared with healthy differentiated cells.

• DNA damage is inherited through cell division. Accumulated damage causes cell death or reduction in reproduction rate.


X-ray, Electron, Proton and Ion Therapy

Relative depth dose curves in water (a) electron beams (b) photon beams (from – Review of Oncology Radiation Physics, 2003) and (c) protons and (d) ions showing Bragg peak (from P. Bryant – CERN)

(a) (b) (c)

(d)


Diseased and normal tissue

• Modern techniques – critical normal tissues e.g. brain, eyes, spinal cord, kidneys, liver, etc. may be completely avoided or irradiated at low levels

• Unless tumour is close to sensitive tissue e.g. brain for brain tumours, spinal cord for cervical or mediastinal tumours


Protons and carbon ions

• Charged particles interact by inelastic collisions with electrons in the medium

• Bragg peak: Energy loss vsdistance Bethe-Bloch formula

4 22 2 2212

1

2

4 2ln ln(1 ) (relativistic term)

Z atomic number of ionZ atomic number of target

mean ionisation potential

e

dE e Z mvZdx m v I

I

π β β⎡ ⎤

− = − − − +⎢ ⎥⎣ ⎦


Ion radiation therapy

• HIT – Heidelberg Ion Radiation Therapy Centre (€119m) – opened in 2009

• Treat brain tumours• 670 ton gantry – 3 MW

power demand – football pitch footprint

• 5 minute treatment time + 20 minutes preparation (1300 patients per year)


Universitätsklinik für Strahlentherapie und Strahlenbiologie, AKH, Wien

Glandula parotid cancer

Comparison of treatment: how to localize dose

Photons 2 fields Photons 5 fields Protons 3 fields


Cure Rates

• Patients with localised tumour at the first consultation (65%)

• cured by surgery 22%• cured by radiotherapy 12%• cured by combination of surgery and

radiotherapy 6%• Patients with inoperable or metastatic disease at

first consultation (35%) – 5% cure rate• Total cure rate: 45%


Oncology


Gantries are huge

• Conical (IBA) and cylindrical (GSI) gantries for ion transport and focussing (from Bryant – CERN)

• 100’s tons


Nuclear Gamma Imaging

• PET and SPECT scans -radioactive isotopes to determine cellular/tissue change.

• Radionuclides are absorbed by healthy tissue at a different rate to diseased tissue.

• A deviation in absorption indicates abnormal metabolic activity.

• X-rays, CT Scans, and MRI can only image structure (e.g. anatomy), not function or metabolism.

PET Scans (Siemens)

SPECT scans


PET scans• Positron Emission Tomograph PET used by cardiologists,

neurologists, and oncologists.

• PET uses positron emitters (F-18, C-11,...), this positrons annihilate with electrons to produce two gamma-rays emitted 180° apart.

• PET imaging maps biological function and detects subtle metabolic changes to determine active or dormant disease and whether a tumour is benign or malignant.

• PET - inject a radionuclide tracer specific to the function or metabolism to be investigated.

• Tracer concentrates in a specific area of the body.

• Detectors in a 360-degree ring detect gamma rays emitted from internal body tissues.

• Data processed to produce cross-sectional images.

• PET requires advanced computer processing, a cyclotron, and trained specialists.


SPECT

• Single Photon Emission Computed Tomography (SPECT) provides information on blood flow to tissue.

• A SPECT isotope (Tc-99m) only emits one gamma ray.

• Sensitive diagnostic tool for detecting stress fracture, spondylosis, infections and tumours.

• Analyzing blood flow to organ helps determine its functioning.

• Radionuclide injected intravenously.

• Tissues absorb radionuclide as it is circulated in the blood.

• Camera rotates around patient and detects gamma photons.

• The images are vertical and/or horizontal cross-sections of the body part and can be rendered into 3-D format.


Medical Radioisotopes

application of laser-plasma accelerators

Documents